The present invention relates to optical communication systems, and more particularly to a narrow band incoherent superluminescent source useful for providing optical carriers.
The optical communications field is expanding at a rapid pace. Telecommunication, sensors, medical and video transmission can all take advantage of optical technology, particularly where virtually unlimited bandwidth and low attenuation are beneficial. Cable television systems are one example where optical fiber technology is providing efficient and economical alternatives to prior coaxial cable distribution schemes.
Fiber optic communication systems which utilize direct detection of information signals that are modulated on a carrier do not require a coherent light source such as that produced by a laser. Lasers are used, however, because they are readily available and provide a convenient source of high intensity light. However, lasers tend to be expensive and have various operational drawbacks that render them less than optimum for use in the field
Other light sources, such as the light emitting diode (LED) and the superluminescent diode (SLD) have shown promise as carrier generators for fiber transmission. A basic measure of the usefulness of such incoherent sources for optical communication applications is the radiance (or brightness) of the source as measured in watts of optical power radiated into a unit solid angle per unit area of the emitting surface. To be useful for fiber transmission applications, an incoherent light source must have a high radiance and operate with a narrow bandwidth. Although LEDs and SLDs are known with relatively high radiance parameters, narrow spectral widths of about 1 angstrom (.ANG.) have not previously been disclosed.
When both spontaneous and stimulated emission occur in an LED, its output can be of narrower spectral width and higher radiance than if spontaneous emission alone exists. Such "superluminescent" devices have achieved spectral widths of 20 .ANG. under pulsed operation with a very high pulsed driving current. SLDs with narrower spectral widths are not currently available.
It would be advantageous to provide an incoherent light source for use in fiber optic communication systems that is economical and reliable. It would be further advantageous to provide a superluminescent light source for such purposes, having a narrow line width of about 1 .ANG.. Such a light source should be capable of providing a plurality of optical carriers for use in transmitting separate information signals over an optical communication path.
The present invention provides a narrow band incoherent optical source having the above-mentioned advantages.